In some cases, effects of gravity may adversely affect an experimental or industrial process. In such cases, it is often desirable to perform the process in a microgravity environment. When a system is in a microgravity environment, all components of the system are subject to identical or indistinguishable gravitational forces. For example, the system may be in free fall or in orbit about a massive body. In this case, a gravitational contact force between two components of the system, or weight, is absent or negligible.
When the process does not require more than a few seconds of microgravity, the process may be performed in a drop tower or similar facility. Slightly longer processes, e.g., that require nor more than about half a minute of continuous microgravity, may be performed aboard aircraft that fly in an appropriate pattern (e.g., parabolic arcs). Processes that require longer periods of microgravity (e.g., hours, days, or longer) may be performed aboard unmanned or manned spacecraft.
In some cases, a system for performing the process in microgravity may utilize lab-on-a-chip technology or other micro-technology. Use of such technology may enable incorporation of the microgravity system in a platform where available space may be very limited or expensive.
Some such processes require use of liquid materials. A process may require transfer of a liquid from a reservoir to another part of the system, e.g., where the liquid interacts with another component. A process may require transfer of a liquid from the system to a reservoir where the liquid is stored for later use or where a waste liquid is stored. Typically, a flexible liquid reservoir, e.g., in the form of a bag or pouch, enables storage of liquids in a manner that prevents escape of the liquid, conserves space, and enables transfer of the liquid without trapping air or gases which could lead to formation of bubbles.
When a process is performed under normal gravity (e.g., on earth, in an accelerating spacecraft, or in a spacecraft that creates artificial gravity using centrifugal forces), an opening of the liquid reservoir may be placed near the bottom such that gravity causes the liquid to amass at the opening. Thus, applying suction to the opening will readily withdraw the amassed liquid. However, due to the absence of significant gravitational forces in a microgravity environment, a rigid container is not suitable for storing liquids for use by a system. Due to the weightlessness, the liquid, possibly held in a single mass by surface tension, may freely float within the rigid container. In the absence of a force that holds the liquid to a wall of the container, the liquid cannot be drawn by suction into a conduit. Therefore, fluids for use with a microgravity system are commonly held in flexible bags or bladders.